The invention relates to a method and device for increasing the pressure of a gas, in particular of the air delivered by a compressor in a power station, using a booster. As mentioned, the gas may be, in particular, the air which is delivered by a compressor and which is provided by the compressor in a large mass stream and at a high temperature.
In a power station with a system for coal conversion under pressure, compressed air is extracted from the outlet of a compressor and, after a gasification and/or combustion operation at high temperature, is introduced as flue gas into the expander part of a gas turbine. Owing to the coal conversion process, some pressure loss occurs along the path of the compressed air from the outlet of the compressor to the inlet of the gas turbine. In this case, to maintain the necessary distance from the compressor surge limit, this pressure loss should not exceed critical limit values (surge limit curve, operating limit curve) along the path from the compressor outlet to the turbine inlet. In such a power station, then, there may be a very high pressure loss, since, depending on the set-up, particular structural components, such as a device for pressure-type fluidized-bed firing, a coal gasifier, a device for gas scrubbing and/or an afterburner, may be arranged in the path of the air. In the case, for example, of a power station operating with a device for second-generation pressure-type fluidized-bed firing, this pressure loss is of the order of magnitude of 2 bar. Without further measures, this high pressure loss would make it impossible to use a gas turbine of the power output class xe2x80x9cheavy-duty gas turbinexe2x80x9d.
It may be envisaged, then, to overcome the high pressure loss by the installation of a blower or booster.
Such a booster has to be designed for the entire mass stream of air required. However, a booster of this type, such as is available today, for material reasons allows only an operating temperature which is possibly below that of the air flowing in from the compressor. In this booster solution, therefore, where appropriate, it is necessary, in addition, also to have a relatively large and cost-intensive air cooler which has to be connected upstream of the booster. The booster itself is likewise costly because of the unconventional requirements, to be precise, with regard to controlling a very large mass stream, generating a relatively small pressure difference of about 1.5 bar and maintaining high temperatures.
The object of the invention, accordingly, is to specify a method and a device of the type initially mentioned for increasing the pressure of a gas, in which use is likewise made of a booster or a blower, but in which the desired pressure increase can be achieved comparatively cost-effectively.
Where the method is concerted, this object is achieved, according to the invention, in that the mass stream of the gas is subdivided into a smaller part stream and into a larger part stream, in that the smaller part stream is delivered via the booster to an ejector and is combined there with the larger part stream which is supplied to the suction nipple of the ejector, and in that the combined mass stream of the gas is picked up at the outlet of the ejector.
In order here, where appropriate, to protect the booster against temperatures which are too high, there is provision, according to a development, for the smaller part stream to be cooled before delivery to the booster.
The smaller part stream can be approximately 20 to 40% of the mass stream of the delivered gas.
In the power station sector, the mass stream ratio is dependent on the component design.
It is advantageous if the smaller part stream occurring at the outlet of the booster is smoothed with respect to pressure fluctuations.
For the initially mentioned application of the method in a power station, with a device for second-generation pressure-type fluidized-bed firing, it is particularly advantageous if the pressure difference in the mass stream before subdivision and after combination is such that the pressure loss occurring between the outlet of the compressor and the inlet of the gas turbine is not only reduced, but is compensated virtually completely.
The device, provided for achieving said object, for increasing the pressure of a gas is distinguished, according to the invention, by a stream divider, by means of which the mass stream of the gas can be subdivided into a smaller part stream and into a larger part stream, by an ejector, to which the smaller part stream can be delivered via the booster, and by a bypass line, via which the larger part stream can be delivered to the suction nipple of the ejector.
Should the delivered gas stream have a temperature which is too high, so the booster would be put at thermal risk, there is provision, according to a development, for the smaller part stream to be delivered to the booster via an air cooler.
According to a further advantageous design, there is provision for the booster to be connected to the ejector via a line, to which a buffer tank is connected for the smoothing of pressure fluctuations.
The outlet of the ejector may be connected, in a power station, to various components which require the increased-pressure gas, in particular air, for their operation.
Further advantageous refinements are characterized in the subclaims.